1. Technical Field
The present invention relates to an autofocus system, and relates, in autofocus systems for automatically tracking an AF frame, particularly to an autofocus system for performing tracking through face direction determination processing when a plurality of persons moving in a photographic scene pass across each other or pass in front of another person.
2. Related Art
Generally, in autofocus (AF) systems for automatically adjusting the focus of a camera, the camera needs instruction on where to focus. In general cameras, the focusing position is fixed in the center of a photographing area, for example a person and the like at the center of the photographing area are made to come into focus. In addition, as an autofocus (AF) method, there is used a contrast method of detecting the contrast of a subject image from an image signal acquired by the image pickup device and automatically adjusting the focus to a best focus state by controlling the focal length of a photographic lens so as to maximize the contrast.
The area of a subject as an AF target in the photographing area of a camera or the on-screen area of a subject as an AF target on a screen of the reproduced photographing image of a camera is defined as an AF area. In addition, the frame indicating the outline of the AF area is defined as an AF frame.
However, when a moving subject is photographed, it is not preferable that the focusing position is fixed as described above. For example, when a quickly moving subject in sporting scenes may be photographed by a television camera and the like, it is required to detect and track the target subject to be brought into focus in the photographing image.
For example, Patent Document 1 (JP-A-2006-258944 corresponding to US-A-2006/0210260) and the like disclose systems capable of automatically tracking an AF frame by storing a subject image of the focusing target (the in-focus target) as a reference pattern, detecting an image which is the best match to the reference pattern image in the photographing image of the newly acquired frame in a pattern matching method, and detecting the position of the target subject.
However, in the autofocus systems for automatically tracking the AF frame, there is a problem in that tracking fails or a person who is not a tracking target is tracked when a plurality of persons pass across each other or another person passes across the front of the tracking target person on the screen.